In U.S. Pat. Nos. 5,844,086 and 6,005,076 (“Murray II”), assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there is described a process for the isolation of protein isolates from oil seed meal having a significant fat content, including canola oil seed meal having such content. The steps involved in this process include solubilizing proteinaceous material from oil seed meal, which also solubilizes fat in the meal and removing fat from the resulting aqueous protein solution. The aqueous protein solution may be separated from the residual oil seed meal before or after the fat removal step. The defatted protein solution then is concentrated to increase the protein concentration while maintaining the ionic strength substantially constant, after which the concentrated protein solution may be subjected to a further fat removal step. The concentrated protein solution then is diluted to cause the formation of a cloud-like mass of highly aggregated protein molecules as discrete protein droplets in micellar form. The protein micelles are allowed to settle to form an aggregated, coalesced, dense amorphous, sticky gluten-like protein isolate mass, termed “protein micellar mass” or PMM, which is separated from residual aqueous phase and dried.
The protein isolate has a protein content, on a dry weight basis, (as determined by Kjeldahl Nx 6.25) of at least about 90 wt %, is substantially undenatured (as determined by differential scanning calorimetry) and has a low residual fat content. The term “protein content” as used herein refers to the quantity of protein in the protein isolate expressed on a dry weight basis. The yield of protein isolate obtained using this procedure, in terms of the proportion of protein extracted from the oil seed meal which is recovered as dried protein isolate was generally less than 40 wt %, typically around 20 wt %.
The procedure described in the aforementioned patents was developed as a modification to and improvement on the procedure for forming a protein isolate from a variety of protein source materials, including oil seeds, as described in U.S. Pat. No. 4,208,323 (Murray IB). The oil seed meals available in 1980, when U.S. Pat. No. 4,208,323 issued, did not have the fat contamination levels of canola oil seed meals, and, as a consequence, the procedure of U.S. Pat. No. 4,208,323 cannot produce from the current oil seed meals processed according to the Murray II process, proteinaceous materials which have more than 90% protein content. There is no description of any specific experiments in U.S. Pat. No. 4,208,303 carried out using rapeseed (canola) meal as the starting material.
U.S. Pat. No. 4,208,323 itself was designed to be an improvement on the process described in U.S. Pat. Nos. 4,169,090 and 4,285,862 (Murray IA) by the introduction of the concentration step prior to dilution to form the PMM. The latter step served to improve the yield of protein isolate from around 20 wt % for the Murray IA process.
In copending U.S. patent application Ser. Nos. 60/288,415 filed May 4, 2001, 60/326,987 filed Oct. 5, 2001, 60/331,066 filed Nov. 7, 2001, 60/333,494 filed Nov. 26, 2001 and 60/374,801 filed Apr. 24, 2002 and filed May 3, 2002, all assigned to the assignee hereof and the disclosure of which are incorporated herein by reference, there is described further improvements on these prior art protein isolation procedures as they apply to oil seeds to obtain improved yields of dried isolated product protein in terms of the proportion of the protein extracted from the oil seeds which is recovered as protein isolate and to obtain protein isolate of high purity, usually at least about 100 wt % at a Kjeldahl nitrogen (N) conversion rate of Nx 6.25. As used herein, protein content is determined on a dry weight basis. The procedure is employed particularly to produce a canola protein isolate.
In the procedure described in the aforementioned U.S. patent application Ser. Nos. 60/288,415, 60/326,987, 60/331,066, 60/333,494, 60/374,801 and 10/137,391, the oil seed meal is extracted with an aqueous food grade salt solution. The resulting protein extract solution, after an initial treatment with colorant adsorbent, if desired, is reduced in volume using ultrafiltration membranes to provide a concentrated protein solution having a protein content in excess of about 200 g/L. The concentrated protein solution then is diluted into cold water, resulting in the formation of a white cloud of protein micelles which are allowed to separate. Following removal of the supernatant, the precipitated, viscous sticky mass (PMM) is dried.
In one embodiment of the process described above and as specifically described in application Ser. Nos. 60/326,987, 60/331,066, 60/333,494, 60/374,801 and 10/137,391, the supernatant from the PMM settling step is processed to remove a protein isolate comprising dried protein from wet PMM and supernatant. This procedure may be effected by initially concentrating the supernatant using ultrafiltration membranes, mixing the concentrated supernatant with the wet PMM and drying the mixture. The resulting canola protein isolate has a high purity of at least about 90 wt %, preferably at least about 100 wt %, protein (Nx 6.25).
In another embodiment of the process described above and specifically described in application Ser. Nos. 60/331,066, 60/333,494, 60/374,801 and 10/137,391, the supernatant from the PMM settling step is processed to recover a protein from the supernatant. This procedure may be effected by initially concentrating the supernatant using ultrafiltration membranes and drying the concentrate. The resulting canola protein isolate has a high purity of at least about 90 wt %, preferably at least about 100 wt %, protein (Nx 6.25).
In copending U.S. patent application Ser. No. 60/339,350 filed Dec. 13, 2001 and Ser. No. 60/391,046 filed Jun. 25, 2002, assigned to the assignee hereof and the disclosure of which is incorporated herein by reference, there is described a procedure in which enhanced levels of protein from canola oil seed meal is achieved by employing a meal which has been desolventized at a temperature of about 100° C. or less. Such meal may be the starting material for the process of this invention.
In copending U.S. patent application Ser. No. 60/401,782 filed Aug. 8, 2002, assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there is described the recovery of canola protein isolate from the residual meal from solvent extraction of canola oil seed to remove residual quantities of oil, commonly known as “white flake” or less commonly as “marc” meal. Such meal may be used as the starting material for the process of the invention.